Pbogbss oe automatically measuring and apparatus therefor



March 24, 1931. w. A. DARRAH PROCESS OF AUTOMATICALLY MEASURING AND APPARATUS THEREFOR 2 Sheets-Sheet l Original Filed Oct.

a u M a a I 9 3 3 1 a 3 I fl I g 3 u March 24, 1931. w DARRAH Re. 18,005

PROCESS OF AUTOMATICALLY MEASURING AND APPARATUS THEREFOR Original Filed Oct. 29. 1928 2 Sheets-Sheet 2 120 zea H5095 I// T Reissued Mar. 24, 1931 A ENT OFFICE;

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Original noun-140,525,

This invention relates to equipment and methods for automatically measuring differences in light transmission. Among the objects of this invention are to provide economical, simple and quick respondin means for controlling various processes an operations by means of the transparency of certain products which takes place inthe operation.

For example one a plication of thisinvention is the control 0 combustion in order to obtain smokeless combustion, by-the absorption of light through a given column of furnace gases. Another application of this process and'jequi ment is in connection with the filtering or b eaching of solutions such as for example sugar or syrup solutions andfor in:

- stance during the refining operation. I

Another application is in the difference of materials such as dyes for the addition of in '20 (heaters to solutions,.th'e change in light transmission 'of the solution serving to operate an indicator as well as a control.

Anotherapplicationof this device .is th measurement of the thickness of a sheet of material such ajsipaper by the absorption of light of asheet of difi'erent thicknesses. c This process may also beemployed in the application of coatings ,where the thicknessof the coating is controlledbyits power to restrict t ePa sa e Pil h hm s t oati Thisequipment-may, also be employed in suclroperations as the control of density of l Su p nded m t i l. sech e we d Pu p a soluti ou anlaccurate imrnediateresponse .to variationS; in light conductivity ,of ga ses, liquids, solids r-qd s s ene i ndiej pqrmi t n Such r i 99s in l ht. mi qfi ssi nj e qp at c t 1 means for aintaining any desired constant n it onla h eqmpu e r a i li iva sensitiveandm ybe installed without dam "-1 Wm aF u ofone" vv e equipment taaha ege ge i am February i1, 1980,-Seria1 in. since, filed October :9, 1928; A lication ,tor reismeflled December 26, 1980. Serial No. 505,058. I

e'uipment which constitutes my invention a apted to control a liquid or gaseous me-- dium;

Figure 2 shows diagrammatically a portion of the equipment modified to control such a factor as the thickness of a sheet ofpaper during its manufacture; v

Figure 3 shows the relative electrical characteristics occurring durin the operation of my equipment in case of a alance, while Fi re 4 shows the electrical conditions existlng in my equipment in cases of unbalanced or when the control equipment is functioning; v

Figures 5 and 6 show modified arran ements of the apparatus for accomplishing t e results set forth. 7

Referring to Figure 1, 1 represents a source of'light for example an ordinary incandescent light preferably of high intensity. The bulb of lamp'l may be colored to obtain any desired grouping'of'wave lengths which is most satisfactory for the measurements in hand. Ordinarily the shorter wave lengths are desirable and many cases it isan advantage to use for the source of light 1 a mercury arc lamp in a quartz or glasstube. 2 indicates a lens or concentrating device which if desired may be omitted or may be replaced by 'a slotted'screen which is shown also as '3. 4 indicates a mirror which receives the light from source and reflects it'to rotating device 5. Itwillbeunderstood that the object of this equipment is to throw a uniform beam of light intermittently through:

a substance to be'testedl or controlledand a:

standard or comparison substance. L ther-e fore; do not -vvish to be confined teeny-set.

method of accomplishing this result and the equipment indicated where, is shownforpurposesof' clearness and, ease of description many. changes being obviously. possible and still falling within .the scope of this invention.

' Rotating member-"5 carries a series ofmirrors or reflectingmembers such as prisms, so arranged that as the member .5 rotates the beam of light indicated by 6 which falls on pri'sni member 'Z isreflectedtqmirrorfi alter-j nately to pos1tio'n9 and position 10 as shown by dotted lines. As rotary member re-' .volves, the light is passed back and forth between the two points indicated. Rotary member 5 is shown carried in bearing 11 and ing member 5 which are rigidly cou led tother, thus maintaining a definite ase reation between the curent produce by nerator 13 and the travel of the light ray rom rotating member 5.

The light rays from mirror 8 travel alter nately through container 17 and container 18. For purposes of simplicity and description this equipment will be described as being applied to a liquid, but obvious modifications will make the equipment adaptable to either gases or solids. Container 17 is indicated as a standard or check solution carrying a sample of the liquid of the desired density and transparency while container 18 is intended to carry a continual uniform stream of the liquid whose transparency is being checked. 20 indicates a circulating device such as a pump arranged to maintain the liquid in container 17 in agitation both to prevent the settling of insoluble materials and to'eliminate variations due to the agitation of the liquid in container 18.

21 indicates a tank or container holding the material whose transparency is being checked. 22 indicates a duct or pipe taking a sample of the liquid in tank 21 to container 18 for test. 23 indicates another pump or circulating means for returning the sample liquid back to tank 24. If desired, the sample liquid may be allowed to go towaste in which case pump 23 can be neglected.

The light rays after passing alternatelythrough containers 17 and 18 are reflected by means of mirrors 25 and26 to aphoto-electric cell 27 It will be apparent, therefore, that the photo-electric cell 27 is alternately excited by the ray of light first through the sample tube 18 and second through the sample tube 17 thus creating a varying electric current when the rays of light are of unequal photo-electric efiect, but no change of current when the rays of light are of equal photo-electric efiect. Since the solution to be tested and the standard solution are of the same material varying only in density, a

change in density or light absorption ofthe solution being tested will cause a minute current to flow through photo-electric cell 27 when excited by battery 28.

The current passing through photo-electric cell 27 is amplified in any desired ma nne'r principally for the reason that the hoto-elec-I trio currents at present 'availab are too feeble to successfully operate relays or control equipment.

In Figure 1, I have shown dia ammatically a standard three electrodetu 29 similar to amplifiers now used in connection with radio applications or other high frequency equipment. Obviously, if desired, I may emp 0 any other form of am lilier many of which are well known and orm no part of this invention. For purposes of clearness, however I will describe this equipment as illustrated amplifying means. Within tube 29 is placed a grid member30, a filament 31 and a plate 32. The whole equipment is enclosed in a container 33. I

' Filament 31 isqmaintained at the desired operating temperature by means of a battery 34. Plate 32 is connected in series with a coil 35 and a relay member having core 36, armature 37 and an opposin coil 38.

Plate 32 is also connecte in series with a variable resistance 39 and a battery. 40 one terminal of which is connected to filament 31. With the arran ement-described, whenever the potential 0 grid 30 is varied with respect to filament 31 there will be a flow of current between filament 31 and plate 32 in the usual manner, this current bein much greater than the change in potential 0 a grid 30 which is caused b photo-electric cell 27.

Coil 38 is connecte in series with a variable resistance 41 and to the terminals 42 and 43 of enerator 13.

rmature 37 of the relay operates to close contacts 44 and 45 which serve to actuate electrically operated valve 46 or equivalent mechanism.

Automatic valve 46 is connected to a source of liquid 47 by means of piping 48 and dischar es said liquid into tank or container 21 w en .opened.

In operation it will be apparent that a light ray reflected from the mirrors qn rotating member 5 passes alternately throughcolumn 18 and column 17 containing respectively the material to be tested and the standard material. It will be apparent therefore that coil 35 is subjected alternately to, a current impulse which is proportioned first to the light transmitting power of the material to be tested and second to the light transmitting power of the standard material.

The current impulse pro ortional to the light transmitting power oft e standard performs the dual function of'checking the material being tested'with a standard and compensating for variables in photo-electric cell 27 and electrical equipment associated therewith, including the source of light 1, as will hereinafter become apparent.

travel of the ray of light through the vausing a; three electrode tube as the rious mediums to be tested, coil 38 will be subjectedto a flow of current which-will be timed exactlywith the flow of current in coil 35 but op osedin ion.. I

heostat 41and 39 permitadjustment of current flow in coils 35, and, 38 such that the effect on core 36 of the current caused by the light ray traveling through sample medium 17, and the current pro need by the generator 13, simultaneously will be approximatelyequal and opposite.

Impedance 41 and impedance 39 can be normally adjusted so that when the ray of light from the moving reflectorpasses through the standard medium 17 the current flow through coil 35 as a result of the amplified photo electric current from cell 27, would be approximately equal and be 0 posite the current flow from generator 13 an coil 38. Under these conditions the current which results when the ray of light reaches cell 27 from the medium under test will cause an unbalance between coils 35 and 38 if the current in this case is not substantially equal to the current, which resulted when the ray of light passed through the standard medium. As a result therefore my equipment permits of initial adjustment against a set of standard conditions and makes itpossible to choose an set of standarfls which will thereafter be eldautomatica I nder. these conditions the effect of the currents flowin in coils 35 and 38 during the interval ,wi 1 balance and the relay will be unaffected.

If now the current produced by the light sensitive cell 27 when the ray of light travels through the tube 18 isappreciably less than the current produced when the light ray travels through the tube 17 the eifect of coil 35 and coil 38 on core 36 will unbalance.

Armature 37 of core 36 may be polarized. When the resultant magnetic effect on core 36 due to coils 35 and 38" attracts armature 37, contacts 44 and 45 will be closed thus applying a source of potential 51 to automatically operate the valve 46 thus allowing solution to pass from container I, 47 into container '21. v g

It willbe, apparent thereforethatif the opaqueness of the material in tube 18 is greaterthan that in tube 17, the automatic valve 46.will be actuated causing additional liquid to flow into container 2l thusdiluting the material in tube 18, which in turn reduces the opaqueness of this material thus tending to maintain an equilibrium.

An indicating device 52 is shown diagrammatically attached to the circuit, the device serving to give a visual indication of the current flowing through coil 35. Device 52 is preferably constructed in the form of a direct current milliammeter. a a

An understanding of the operation of this equipment can be readily obtained by consid ering Flggures 3 and 4' respectively. Refer- I ring-to igure 3,53 indicates a base lineu n whlch is drawn the curves shown in solid lines and indicated b 54 and 55, and the reverse curves 5 6 and 5 respectively.

In Figure 4, 53 indicates the same base llne'as in Fi ure 3 and other numbers similar parts as in igure 3. Referring,to Figure 3, it mafy be assumed that 54 indicates the curve 0 magnetic efiect produced on core 36 by the amplified current from photoelectric cell 27 when actuated by the standard material; while curve 55 indicates the corresponding curve of magnetic efiect produced on core 36 by-the hoto-electric cell 27, when submitted to the light traveling through the material whose opaqueness it is desired to maintain constant. f Curves 56 and 57 represent the magnetizing effect of coil 38 upon core 36 due to the current wave produced by generator 13 and which it will be noted is synchronized but opposite to the ma netic effect produced by the light rays trave and 18. In Figure 3 it will be noted that curve 54 is equal and opposite to curve 56 and curve 57 is equal and opposite to curve 55 so that there is substantially no resultant magnetic eflect upon core 36 and armature 37 is there fore not lifted and automatic valve 46 is not operated.

Referring now to Figure 4, the condition there illustrated shows the'standard constant wave produced by generator 13 namely curves 56 and 57, and shows also the standard constant wave produced by light traveling through the standard sample in tube 17, namely curve 54. In this case, however, curve 55A represents the magnetizing 'efiectdue to the current generated in photo-electric cell 27 when the light ray travels through the tube 18 containing the medium to be controlled.

In this case, it is assumed that the density of medium 18 has increased which would in turn decrease the transmission of light through tube 18 to photo-electric cell 27 andthus'materially reduce the current passing through coil 35 as a result of such light action. Since the current passing through coil 35 is 'materially reduced, the magnetizing efiectupon core 36 would also bev reduced and this is shown as curve 55A. Since curve 55A is now materially less than curve 57, a balance, is not obtained but a marginal magnetizing which is indicated by the shaded. area 58 is available to operate the relaylifting arma-- ture 50 and thus to cause automatic valve 46 to operate. Obviously operating-automatic valve 46 causes the addition of water from container '47 to container 21 thus diluting the :mixture incontainer 21 and therefore diluting the material in sample tube'18. This promptly results in an increased transing through the tubes 17 slon.

Obviously conditions may be exactly reversed and tank 47 may contain for example a supply of dye or opaque material in which case t e equipment may be employed to maintain the desired opaqueness.

In the description given above, the equipment is used to maintain a uniform condition of light transmission through a liquid or gaseous material. Illustrations of such conditions would be the maintainin of a con stant cor "entration of wood pulp in solution,

or the maintenance of a constant addition of lime to lime water and various other chemicals, dyes, etc.

In Figure 2, a diagrammatic arrangement is shown of a thin solid material such as a strip of paper, cardboard, film, etc. 1 Similar numbers represent similar parts. In Figure 2, A and 61A indicate screens which may be interposed in the path of light ray to obtain the desired color, intensity of light balance. 62A indicates a strip of .solid material which is being tested and 63A a standinstead of manual which is the present prac-' tice. Y

I wish it to be understood that any features shown and described in this specification are to be taken as dia ammatic in being possible to make any su itutions and variations without departing from the spirit of my invention. For example, I may use any desired number of amplif ing tubes or I may use other commercial orms of amplifiers. The relay which I have shown may be constructed in any well known forms all of which come in the sec of my invention. Instead of using the p oto-electric cell indicated in 27 I may use a piece of ii ht sensitive selenium or other material of t is nature althou h'I prefir photo-electric cell of the type mdicate Various forms of generati equipment may be used as for example, a-vi rating type of generator or a vibrated contact in which case of course, the li ht rays would be syn-- chronized with the vi rations of the generating device. Thus I may use a vibrating electro-magnet carrying a mirror on the moving part in place of the system comprised by rotating member 5, generator 13 and motor 15. In this case I may also use the exciting current of vibrating device in coil 38 after propcomes the difiiculties which would normally be inherent in a device of this kind due to variations in the amount of light produced as for example, fluctuations in voltage a plied to the light, deterioration in the lig t source, etc.

This arrangement also avoids variations due to a change in sensitiveness of photo-electric cell 27. For example if the photo cell becomes more or less res onsive,

the changed condition afi'ects botht e reaction of the cell to the light ray from the test medium and the light ray from the standard. Since both reactions are converted into electrical impulses which are opposed to each other, the larger impulse will control the operation of the relay which will he therefore independent of the sensitivity or related characteristics of the cell, but will be controlled entirely by the relative strength of the light ray the test medium. As contrasted to this condition, the ordinary circuit using a photoelectric cell as a simple light sensitive control will give electrical impulses which varywidely in intensity with the condition and age of the cell, the impressed voltage on the cell and light source and many other factors. Obviously, the arrangement which I have disclosed may be operated oil of any standard commercial circuit as for example, the normal lightin circuits and the equipment is simple, readify obtainable and inex ensive.

It is a fact that very large financia wastes occur continuously owing to the lack of means of controlling the concentration of such materials as dyes in the solution, wood, pulp in the. solution, amount of paint or pigma applied to cloth, paper, etc., and other similar cases. I

The application of this equipment to the control of combustion in furnaces as for example in the producing of steam under boilers is evident. Inthis case, the example of the products of combustion from the furnace from the standard and from descent lamp. The light passes from the filament or lamp through a controlled openin in screen 61 to a mirror 62 located on a vi rating member 63. Member 63 may be constructed in any, desired manner as for example, a rugged steel spring securely fas tended at. one end 64 and provided with an adjustable rider 65 arranged to control the period of vibration of member 63. The mirror 62 may be in the form of a prism or any desired reflecting surface. Vibrating member 63 is maintained in vibration during the operation or the device by an alternating current coil 66, actuated from a source of potential applied to terminals 67and 68. Light rays which fall on mirror 62 are reflected to a second mirror 69 and as vibrating member 63' travels the light is passed alternately through container 70 and container 71 which represent respectively, the standard sample and the material being tested and controlled. Light ray passing throu -h' containers 70 and 71 fall on mirrors 72 and 3 respectively, and are reflected to photo-electric cell 74 in the manner previously described. The terminals of photo-electric cell 74 are connected in series with a variable resistance 75 and a source of mary terminals to 67 and 68. Coils 79 serves as one secondary winding for transformer 81 and coil 82 serves as another secondary winding. A sample rectifier such as a vacuum tube 83 is connected in series with the terminals of coil 82 and serves as a'source of potential for photo-electric cell 74 as previously .described and .a source of potential to beapplied between plate 84 of. tube 77 and filament 78; A-variableimpedance 85 is placed in series .with this .circuit the terminals of which are connectedto coil.,86 around core87 of a relay member. Coil 88 is woundaround core, 87. and connected .to secondaryzwinding 82 of transformer 81 in such a manner that the rectified current delivered to coil 88 produces normally a magnetizing effect approximately equal and opposite to that produced by coil 86 when actuated by the amplified photo-electric current of cell 74 under the influence of light rays traveling through tube 70. Obviously, pro r balance under these conditions may be 0 tained by the adjustment of the variable impedances mentioned including variable impedance 90 in series with coil 88.

It will be apparent that as long as the effect on cell 74 by light rays traveling through container 71 is the same as the efl'ect-by lig t rays traveling through container 70, that the magnetizin changes acting on core 87 of the relay w1ll remain balanced and the relay will remain open. As soon, however, as the intensity of light traveling through the two containers 70 and 71 is difl'erent, the magnetizing effects of coils 88 and 86 on core 87 will vary in the manner previously outlined and diagrammatically illustrated in Figures 3 and 4. Under these conditions the core 87 will attractv core 91, closing contacts 92 and 93 and a plying the potential fromterminals 67 and 68 upon the desired automatic control equipment indicated. diagrammatically by the rectangle 94. Automatic control equlpment 94 may be employed as previously explained and described to open valves, close dampers, or perform other control operations. 7 Obviously the arrangement of equipment shown and described in connection with Figure 5, would be understood as diagrammatic and subject to many obvious modifications without departing from the scope of this invention.

The arrangement shown in Figure 6 illustrates another alternate form of my invention. In Figure 6 a ray of light indicated as 100 is directed upon a reflector 101. Reflector 101 is supported by vibrating member 102 which is fastened at one point to supporting member 103. An alternating current electro-magnet 104 is energized by terminals 105 and 106 and causes vibrating member 102 to oscillate continuously. I

Vibrating member 102 carries contacts 107 and 108 arranged to close circuits .respectively throughv windings 109 and-110 as member 102 vibrates. I f g V v The material whose density is beingcon-v trolled is illustrated diagrammatically as being within container 111 while :a standard.

usedfor comparison in container112. i Mirrors113 and 114. respectively directthe beam from ray 100 successively through containers 11 1: and 112. as member 102 oscillates. Mirrors 115 ;and.;116 are arranged: to reflect -,the' .beam -;of=' lightafterf I traveling.

purposes is .held withdescription of the equipment. The 0 'tric cell 117.

throu h containers 112 and 111 respectively, to lig t sensitive cell 117. a

Light sensitive 'cell 117 is connected in series with a source of current 118 and the grid 119 of a three-electrode tube 120 Tube is used to amplify the currents produced in light sensitive cell 117. Obviously any other equivalent amplifying means could be employed Tube 120 is provided with filament 121 actuated from a source of current 122. A plate member 123 in tube 120 serves to receive the amplified electrical impulses which are originated in light sensitive cell 117. The circuit from plate 123 includes filament 121, a source of current 124 vibratin member 102, and alternately contacts 10 and 108, and the respective windings 109 and 110. Windings 109 and 110 are equal in the number of turns, but opposite in direction. Core 124 is arranged to actuate arma ture 126 when the magnetic efiect of windings 109 and 110 is not balanced. .When armature 126 is attracted by core 125 contact 127 is closed, thus actuating automatic valve or other control mechanism 128 by source of current 129. Obviously one or all of the sources of current mentioned in this description may be-combined, individual sources of current being shown in order to clarify the ration of the arran'fgement of equipment s own in Figure 6 is as ollows:

Vibrating member 102 is maintained in synchronous vibration by magnet member 104 or any other suitable means.

As a result of the vibration of member 102 light ray 100 is successively deflected through container 111 and container 112 being alternatel directed upon photo-elechoto-electric cell 117 therefore alternately permits a current to flow in the circuit of the grid member 119. The current flowing in grid member 119 will be roportional to the intensity of the rays of llght assing through containers 111 and 112, and 1f the density of the material incontainers 111 and 112 is such that the light absorption in eachcase is identical, the currents flowing in the grid circuit 119 will be equal for each impulse.

These currents will successively pass through windings 109 and 110 under the influence of current sup 1y member 124.

When vibrating member 102 is at the upper portion of its travel, contact 107 will be closed permitting the current from plate circuit 123 to pass through coil 109. During thissame interval, a light ray of 101 is deflected through container 11130, that the current flowing through coil 109 will be proportional to the opaquenes of material in container 111. I

.On the other hand when vibrating member 102 is at the lower portion of its stroke, conwill be closed, thus permitting the current from plate member 123 v.to pass through coil 110, which, however, is wound in an opposite direction to coil 109. Durin this interval of time, light ray 100 is deflecte throu h container 112 and the current passing t rough coil 110 is therefore proportional to the o aqueness of material in container112. I the opaqueness of the materials in containers 111 and 112 is equal the currents passing through. coils 109 and 110 will be equal and opposite and core 125 will be subjected to an alternating magnetic force which will-not lift armature 126.

If, however, the opaqueness of material in containers 111 and 112 is not equal the curin obtaining a control .may cover a wide range of equivalents such as has been ously described and explained.

It should be understood that in all cases previ- "actuating control where I oppose two varying currents as for exam le in coils 36 38, 86 88, 109-110, etc., t e inertia or time la of the-equi ment normally results in retar in the motion of the circuit closing device, so t at the contacts of the circuit closing. device do not chatter or vibrate excessively. The inertia which accomplishes this result may be physical, that is due to the'delay in accelerating closing device, etc., it may be ue to fric-' tion, or it may be of the nature of electrical or magnetic inertia of various parts of the equipment or circuit. The effect ofthe inertia is in fact so difficult to eliminate that it ma be asumed to be present in nearl all ractical devices when 0 erating' at i'gh equencies. Of course t e inertiaeflect whether due to physical magnetic or electrical forces will increase, with increase'in the frequency with which the electric currents are imposed on the circuit closing device.

It will be apparent that the system de-.

scribed in this specification is independent of-such'variables of applied potentials, de-

-terioration of light source, change in activity of photo-electric cell, variation' of amplifiers,

etc. In. other words the equipment-which the circuit I have invented gives constant results. under all practical commercial conditions and independently of the usual variables which are normally encountered. .4

Having now fully described my invention,

said currents against constant s nchronized' opposin currents so arranged t at a van.- tlon in t e opaqueness of the material being controlled Wlll unbalance said currents and thus actuate a device for correcting the density of said material being controlled.

2. A device for controlling the density of a medium consisting of a source -of light, means for directing rays from said source of light succesively through a standard and said medium being controlled, light sensitive means actuated by said rays to produce a current varying with the opaqueness of said material beingrtested, a relay actuated by saidvaryin currents, a winding on said relay actuate current and a control equipment actuated by said relay for controlling the density of the material being tested.

3. In a device for automatically controlling materials, a device for successively deflecting a ray of light, a light sensitive relay and a control device actuated by said light sensitive relay.

4. In a process of automatically controlling the concentration of materials in solution, the stepof passing a beam of light successively through a sample of material to be controlled and a standard sample, producing electrical forces proportional to the strength of said light rays, and balancing said electrical forces against synchronzied opposing electrical forces.

5. The process of automatically controlling the concentration of wood pulp in water whlch consists in passing a ray of light successively through a sample of material to be controlled, and a standard, causing said ray of light to actuate a light sensitive relay and causing said relayto increase the quantity of water mixed with said wood pulp.

6. In the process of controlling the concentration of a medium in, a fluid, the step of passing a ray of'light, successively through the medium to-be tested and a standard and balancing the efiect produced by said ray of light after passing through said medium to be tested against the effect produced after passing through said standard.

7. The process of automatically controlling the concentration of material in solution. by

passing a light my successively through the solution to be tested and a standard,bal-" by a synchronized opposingthe unbalanced component to operate a control device. I

8. The process of controlling the opaque ness of a material which consists of first passing alight ray from a common source successively through the material being controlled and a standard material, second directing said light rays to cause the flow of current froma device, third balancing said currents thus produced respectively against a pair of synchronized opposing currents of fixed value, and finally causing an unbalance between said balancing currents and said light currents, to operate a control device for restoring uniform opaqueness.

9. The process of automatically controlling the opaqueness of a material by passing a ray of light successively through said material and a standard, causing the variation of the light ray thus passed to actuate a control device for automatically maintaining con- I stant opaqueness.

10. The process of automatically controlling the concentration of material in suspension in a fluid by passing a ray of light successively through the stock to be tested and a standard agitated sample of-stock, causing said light ray to actuate a light sensitive relay and causin said relay to actuate a control device for c anging the concentration of material in suspension. a

11. The process of automatically controlling the concentration of pulp in suspension in a fluid by passing a ray of light successively through said stock to be tested and a standard sample of stock, causing said light ray to actuate a light sensitive relay, and causing said relay to actuate a control device for changing the concentration of the material. in suspension.

12. A device for automatically controlling materials comprising. a light source, a light deflecting device, a light sensitive device, a relay device and a control mechanism actu-- ated by differences in light intensity from said li ht deflecting device.

13. device for automatically controlling materials consisting of a synchronized light deflecting device, a light sensitive device, and a control mechanism actuated by difierence in light intensity from said synchronized light deflecting .device.

14. A device for automatically controlling the concentration of materials suspended in a fluid, consisting of a light producing device, a moving light deflecting device, alight sensitive-relay, amplifying means, and a mechanism actuated from said light sensitive relay for automatically changing the concentratlon of said material.

15. A process for automatically controlling the properties of a material including;

the stepsof passing a beam of lightsuccessively through the material and a standard and. utilizing the unbalanced component o the light rays for operating a control device for sald material.

16. In the process of automatically controlling properties of materials by their light transmission, the step of passing a beam of light successlvely through the materialto be controlled and a standard.

17. A process for automatically controlling properties of materials by their light transmission, includin the steps of passing a beam of light successively through the material being controlled and a standard, and utilizing the resultant difierential for controllin the properties of said material.

18. n a process for controlling the properties of materials by their light transmission, the step of intermittently checking the light transmission of the material being controlled with a standard.

19. In a measuring or controlling device, a photo-electric cell subject to variations in its current response for light rays of a given intensity, in combination, automatic operating means to compensate for said variations in the current response of said cell.

1 20. In a measuring or controlling device, a photo-electric cell subject to variations in its current response for light rays of a given intensity, a current responsive device connected with the cell, and automatic operating means whereby said variations in the response current of the cell will be compensated in the operation of said current responsive device.

v21. An apparatus for automatically controlling materials by'their light transmission comprising a source of light, a means for supplying impulse current, a combined light ray deflectin device and current impulse control, a lig t sensitive cell and a material in the path of deflected rays, and means for utilizing the current impulses from the current impulse control and the cell for controllin said material.

22. n apparatus for automatically controlling materials by their light transmission com rising a source of light, a means for supp y impulse current, a light ray, a synchronously operated light ray deflecting device and current impulse control, a light sensitive cell and a material in the path of the deflected rays, and means for utilizing the current impulses from the currentimpulse control and the current impulses from the cell for controlling the material.

23. In a measuring or controlling equipment empl oying a source of light, a h-ght sen-.

sitive ce and electrical devices responsive to currents from the light sensitive cell, in.

combination, automatic operating means for checking each measuring or controlling operationof the equipment.

24. In a measuring or controlling Milligment a source of light, a g t sensitive and electrical devices responsive to currents from the light sensitive cell, in combination, automatic operating means for checking each measuring or controlling operation of the equi ment and/or compensating for variables in t e equipment for each measuring or controlling operation thereof.

25. In combination, a light source, a light sensitive cell, a multiple of light paths by which light from 'said source may reach said cell electrical ofperated equi ment responsive to the current rom said ce and automatic means for intermittently subjecting said cell to light rays from each of said multiple of to respond to rays of light of known mtensity for each resfionse thereof to the light rays being contro ed or measured, and means for balancing the resultant current responses of said cell against each other.

28. In a controlling or measuring device, a light-source, a light sensitive cell, a pair of paths by which hght from said source may reach said cell, automatic operating means for alternately subjectin said cell to light rays from said light pat s, and electrically operated devices connected to the cell and responsive to the currents therefrom for efiecting the measuring orv controlling operations of said equipment.

29. In a controlling or measuring device, a li ht source, a li ht sensitive cell, a plurality 0? paths by which light from said source may reach said cell, automatic 0 crating means for subjecting said cell at-di erent intervals to light rays from each of said paths, and electrlcally operated devices connected to said cell and responsive to the current thereof for efiectin the controlling or measuring operatlons 0 said equi ment.

30. In a contro ing or measuring device, a

ht source, a li ht sensitive cell, a plurality paths b whic light from said source may reach sai cell, at least one of said paths being adapted to limit the light rays reaching the cell to substantially constant intensity, automatic 0 rating means for subjecting said cell at 'fl'erent intervals to light rays from each of'said paths, and electrically. operated devices connected to said cell and responsive to the current thereof for effecting t e controlling or measuring operations of said 'uipment.

31. a controlling or measuring device, a

light source, a li ht sensitive cell a plurality of paths b whic light from said source may reach sai cell, automatic operating means for subjectingsaid cell at difierent intervals to light rays fromeach of said paths, and electrically operated devices connected to said cell and adapted for combining current impulses from said cell and effecting the controlling or measuring operations of said equipment therewith.

32. In a measuring or controllin equi ment employing a source of light, an a lig t sensitive cell, in combination, automatic operating means for causing the light sensitive cell to emitacheckingcurrentimpulse for each measuring or controllin current impulse, and electrically operated evices connected to the cell and adapted to effect the measuring or controlling operations of said equipment in accordance with said cell current impulses.

33. In a measuring or controllin equipment employing a source of light, and a light sensitive cell, in combination, automatic 0pcrating means for causing the light sensitive cell to emit a checking current impulse for each measuring or controllin current impulse, and electrically o erate devices connected to said cell adapts to combinethe current impulses from said cell and utilize the I combined current im ulses for eflectin the measuring or control 'ng operations 0 said equipment.

WILLIAM A. DARRAH. 

